The invention concerns an implantable electrode which includes at least one electrical conductor having a proximal connecting region for a pulse generator and at least one working electrode which can be connected to the pulse generator by way of the conductor.
Electrodes of the general kind set forth are well-known from the state of the art. They are a component part of numerous functional electrostimulation devices (FES) which are used for the electrical treatment of nerve or muscle cells in the diagnostic or therapeutic sector. Implant systems for functional electrostimulation, include for example, cardiac pacemakers with a pulse generator for artificially stimulating cardiac actions, which is disposed in a body-compatible housing with associated electronic circuit and power supply. The housing has a connecting location to which the electrode is connected.
The term ‘electrode’ in medical technology denotes not only the transfer location for electrical energy in accordance with the physical definition but also relates to the line comprising the electrical conductor together with encasing insulation and all further functional elements which are fixedly joined to the line. Hereinafter, for purposes of clarity, the portion of the electrode which actually acts in the physical sense and which includes the transfer location for the electrical energy is referred to as the ‘working electrode’.
The materials which are suitable for the purposes of such use should enjoy adequate bioresistance and also good biocompatibility. Accordingly it is necessary to ensure that long-term implantation in the body—that is to say in a highly corrosive environment—occurs without noteworthy breakdown processes and does not result in an unwanted immunological reaction. Biocompatible plastic materials based on silicone, polycarbonates, epoxysilanes, polyurethane, polysulfones, polyethylene and polyester present themselves as suitable for insulation of the electrical line. The working electrodes in turn which can be designed in the form of discharge, stimulation and measuring electrodes are generally formed on the basis of biocompatible metals such as platinum, iridium, titanium or gold.
Materials for use in implants are acceptable when the surrounding tissue reacts to mechanical disturbing influences and the presence of the material only to a slight extent with non-specific inflammation phenomena, even with an increased risk of allergy.
It has been found that tissue regions which are exposed to mechanical disturbing influences have a tendency to involve an increased immunological reaction or inflammation reaction. Electrodes have such regions inter alia at the connecting locations to the housing of the pulse generator as it is there that the geometries of the components impose limits on ‘mechanically flexible deflection’ of the electrode. A further area involving a particular loading is in the region of the working electrodes which in fact, to perform their function, must bear directly against the tissue to be stimulated. Here too unwanted immunological and inflammation reactions on the part of the body repeatedly occur. In addition electrodes frequently have to be provided with anchor elements or holding structures in order to ensure a relative spatial position of the working electrode with respect to the tissue to be treated. Immunological and inflammation reactions generally occur to an increased extent also in the regions of the holding structures and anchor elements which can be of many different configurations.